1. Field of the Invention
The present invention relates generally to color photography and more particularly it relates to a multilayer color photographic material having excellent color reproduction and sharpness.
2. Description of the Prior Art
A silver halide color photographic material based on the three primary color principle of the subtractive color process is fundamentally composed of a silver halide emulsion layer which is colored yellow by the action of blue light, a silver halide emulsion layer which is colored magenta by the action of green light, and a silver halide emulsion layer which is colored cyan by the action of red light.
It is well known that compounds forming dyes such as indophenols, indoanilines, indamines, azomethines, phenoxazines, phenazines, etc., by the coupling reaction with an oxidized primary aromatic amino developing agent, which compounds are called couplers, are used as color formers for such color photographic materials.
In the above described color photographic materials, acylacetamide derivatives or dibenzoylmethine derivatives are used as yellow forming couplers, 5-pyrazolone derivatives, cyanoacetyl derivatives, indazolone derivatives, or pyrazolobenzoimidazole derivatives are used as magenta forming couplers, and phenol derivatives or .alpha.-naphthol derivatives are used as cyan forming couplers.
Ideally, in such color photograhic materials based on the three primary color principle of the subtractive color process, the yellow dye image formed absorbs blue light only, the magneta dye image absorbs green light only, and the cyan dye image absorbs red light only. However, the dye images obtained in color photograhic materials using these couplers do not always correspond to the ideal, that is, they have frequently side absorptions and additionally absorb light in other wavelength regions.
A masking process using a colored coupler for correcting the desired absorption of the dye images as described in, for example, PSA Journal, Vol. 13, 94 (1947), is well known.
The dye image obtained from a phenol derivative or a naphthol derivative used as a cyan forming coupler has a main absorption in the red region of from about 600 nm to about 800 nm and also a side absorption in a blue wavelength region of about 440 nm. Also, to correct the side absorption, use of a phenol type or .alpha.-naphthol type colored coupler in which the phenol or .alpha.-naphthol nucleus has been substituted with an azo group at the para-position to the hydroxyl group thereof is known. However, such a para-azo substituted phenol or a .alpha.-naphthol colored coupler usually has an insufficient color and, in particular, couplers of the above type having a sufficient color for correcting the side absorption in the green wavelength region have not yet been discovered.
Also, the dye image obtained from a 5-pyrazolone derivative used as a magenta forming coupler has a main absorption at a green wavelength region of from about 450 nm to about 550 nm and side absorptions in the red wavelength region and the blue wavelength region. To correct the side absorptions, use of a 5-pyrazolone colored coupler in which the 4-position of the 5-pyrazolone nucleus has been substituted with an azo group is also known. However, 4-azo substituted 5-pyrazolone colored couplers usually have insufficient color and, in particular, couplers of the above type having a sufficient color for correcting the side absorption in a red wavelength region have not yet been discovered.
Furthermore, conventional azo-substituted colored couplers as indicated above have a slow rate of reaction with an oxidized primary aromatic amino developing agent and hence provide an insufficient masking effect.
Still further, the color of conventional azo-substituted couplers changes as the pH of the processing solution is varied and hence they do not provide a stable color.
U.S. Pat. No. 3,476,563 discloses a naphthol coupler having structure (A) shown below: ##STR1## as a coupler for masking the blue wavelength region of a cyan dye image.
Since a coupler of this type shows a high masking effect and less change in color due to changes in the pH of the processing solution, the above defects of azo-substituted colored couplers can be overcome but the coupler has the difficulties that fog is formed in the photographic emulsion layers and the granularity of the silver halide emulsions is reduced.